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I think Intel's iAPX 432 was probably the last in ~1982. It's not just that the RISC philosophy became popular, but suddenly it didn't make much sense to desig
by phire 3y ago
I think Intel's iAPX 432 was probably the last in ~1982.
It's not just that the RISC philosophy became popular, but suddenly it didn't make much sense to design a CISC ISA anymore.
CISC was a great idea when you had really slow and narrow RAM. It made sense to try and make each instruction as short and powerful as possible, usually using microcoded routines. But RAM got cheaper, buses got wider and caches started being a thing. It didn't make any sense to waste transistors on microcode, just put them all in RAM.
- userbinator 3y agoInstruction cache usage is still important, especially with memory latencies being what they are today.
- syntheweave 3y agoIt was a combination of the material factors and a mindset shift towards higher-level programming as the default. The appeal of CISC instruction sets when marketing to programmers lies in their batteries-included stance: they handle more of the binary encoding stuff for you, more of the math operations. With a RISC approach they have to write library code to do the same tasks, which adds some implementation complexity as well as potentially being most of the size of a short program. And that makes sense - if you expect direct instruction encoding to be the whole programming environment, which, for the first computers, it had to be. By the time you get to the microcomputer era the balance had shifted pretty resoundingly towards working at a higher level - that's why nearly every machine of that generation had a BASIC, and if you have a BASIC it's more important for the instruction set to be efficient, because efficiency becomes the only reason to drop down from a high level environment.